Electron-Spin Dynamics and Structures in Halogen-Bridged 1-D Metal Complexes Studied by Solid NMR

Magnetic properties characteristic in 1-D systems were investigated in halogen-bridged mixed-valence and averaged-valence metal complexes by applying magnetic resonance techniques. Neutral-solitons and polarons formed from impurity amounts of paramagnetic Pt3+ and Pd3+ sites in 1-D chains were sensitively detected by the NMR relaxation measurement. Their rapid 1-D diffusion comparable to that in trans-polyacetylene was revealed in [MII(en)2][MVIBr2(en)2](ClO4)4 (M: Pt, Pd). From 13C NMR spectra and 1H NMR relaxation studies, [NiIIIX(chxn)2]X2 (X: Cl, Br) was shown to be in an averaged-valence state forming S = 1/2 1-D Heisenberg antiferromagnetic chains. [NiBr(chxn)2]Br2 revealed to have the largest exchange interaction so far reported, was expected to transform into a new state at low-temperatures below 100 K. From studies on thermal motions and phase transitions associated with the 1-D chain-structure in [Pt(en)2][PtX2(en)2](ClO4)4 (X: Cl, Br), the presence of the dynamic disorder of the Pt(en)2 chelate-ring conformation in a highly asymmetric double-well potential undetected by the X-ray diffraction was detected by the NMR relaxation measurement.